1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine that has a variable valve mechanism that varies valve characteristics of an air intake valve and particularly relates to a control apparatus and control method for an internal combustion engine having a lift amount change mechanism and a valve timing change mechanism as variable valve mechanisms.
2. Description of the Related Art
An internal combustion engine equipped with a variable valve mechanism that changes valve characteristics of an air intake valve according to engine operational state is being put into practical use. As this type of variable valve mechanism, a valve timing change mechanism is widely known that changes valve timing of an air intake valve that is opened and closed by a cam shaft by changing a rotation phase of the cam shaft relative to a crank shaft.
In recent years, a lift amount change mechanism has been proposed (Japanese Patent Application Publication No. 2001-263015 (JP-A-2001-263015)) that is made capable of continuous change of a maximum lift value and lift time by continuous change of the lift amount of the air intake valve. In this lift amount change mechanism, the lift amount becomes maximum when a movable part becomes positioned at a movable limit position at one side within a specified movable range. Then, by changing a position of the movable part in this movable range, the lift amount of the air intake valve is varied. The control apparatus of an internal combustion engine having this type of lift amount change mechanism detects the present lift amount based on an accumulated movement of the movable part from a base position that is set based on the movable limit position where the lift amount becomes largest.
The internal combustion engine having this type of lift amount change mechanism and the abovementioned valve timing change mechanism changes valve timing according to lift amount of the air intake valve set by the lift amount change mechanism (i.e., performs coordinated control of the lift amount change mechanism and the valve timing change mechanism). By this means, the valve timing and the lift amount of the air intake valve can be finely controlled according to the engine operational state, and improvement of output, fuel consumption, and exhaust properties is possible.
However, the control apparatus of an internal combustion engine having the above type of lift amount change mechanism sometimes becomes unable to recognize the lift amount when a sudden blackout (i.e. a so-called instantaneous interruption) of the electrical power supply occurs due to failed connection of the electrical power line for supplying electrical power to the control apparatus and the like and the accumulated movement of the movable part recorded in memory disappears. Moreover, when the displacement amount of the movable part has changed for some reason during engine stoppage during which electric power is not supplied to the control apparatus and displacement amount of the movable part is not monitored, a discrepancy arises between the lift amount understood by the control apparatus and the actual lift amount.
When a discrepancy arises between the lift amount understood by the control apparatus and the actual lift amount in this manner, and the control apparatus therefore becomes unable to accurately understand the actual lift amount, valve timing set based on the lift amount understood by the control apparatus becomes unsuitable for the engine operational state. This results in instability of the engine operational state, and there is concern that this may cause the occurrence of misfiring, knocking, and the like in some cases.
Specifically, when the valve timing of the air intake valve has been shifted to the advance side in a state where the lift amount of the air intake valve is extremely large as indicated in FIG. 14A, since air intake valve open time IVO becomes early, valve overlap becomes excessively great, and the internal EGR amount increases. This results in an insufficient supply of oxygen for combustion, combustion instability, and a greater risk of misfiring. Moreover, when the valve timing of the air intake valve is shifted to the delay side in a state where the lift amount of the air intake valve is extremely small as indicated in FIG. 14B, the valve open time IVO of the air intake valve is at or after the top dead center, and the valve close time IVC is in the vicinity of the bottom dead center. As a result, negative pressure in the combustion chamber at the valve open time of the air intake valve increases, the flow speed of air introduced to the combustion chamber increases at this time, and the air intake valve is closed and compression is started in the vicinity of the bottom dead center, which result in increase of temperature and pressure within the combustion chamber, and a greater risk of knocking.